U.S. patent number 6,903,529 [Application Number 10/677,127] was granted by the patent office on 2005-06-07 for method and apparatus for damping mechanical oscillations of a shaft in machine tools, manufacturing machines and robots.
This patent grant is currently assigned to Siemens Aktiengesellschaft. Invention is credited to Stefan Kunzel, Theo Reichel, Elmar Schafers, Andreas Uhlich.
United States Patent |
6,903,529 |
Kunzel , et al. |
June 7, 2005 |
**Please see images for:
( Certificate of Correction ) ** |
Method and apparatus for damping mechanical oscillations of a shaft
in machine tools, manufacturing machines and robots
Abstract
Damping of mechanical oscillation in a shaft that is provided by
feedback wherein the output signals of multiple feedback devices
are negatively coupled and added to a desired speed signal of a
motor speed controller of the driving motor is disclosed. At least
one sensor and/or measuring system can be provided for measuring an
actual position value. The actual speed of the shaft can be
determined by differentiation from the shaft position value
measurements or by integration from shaft acceleration
measurements. The measured or actual speed of the shaft can be
supplied as an input signal to each feedback element. Each feedback
element is specifically tuned to an oscillation frequency range of
the shaft that is to be damped. The invention provides an easy and
cost-effective way of damping mechanical oscillations that have
limited frequency ranges.
Inventors: |
Kunzel; Stefan (Erlangen,
DE), Reichel; Theo (Forchheim, DE),
Schafers; Elmar (Nurnberg, DE), Uhlich; Andreas
(Wendelstein, DE) |
Assignee: |
Siemens Aktiengesellschaft
(Munchen, DE)
|
Family
ID: |
29285743 |
Appl.
No.: |
10/677,127 |
Filed: |
October 1, 2003 |
Foreign Application Priority Data
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Oct 2, 2002 [DE] |
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102 46 093 |
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Current U.S.
Class: |
318/611; 318/609;
318/610; 318/615 |
Current CPC
Class: |
F16F
15/005 (20130101); F16F 15/02 (20130101); G05B
19/404 (20130101); G05B 2219/37493 (20130101); G05B
2219/37525 (20130101); G05B 2219/41121 (20130101) |
Current International
Class: |
F16F
15/02 (20060101); F16F 15/00 (20060101); G05B
19/404 (20060101); G05B 005/01 () |
Field of
Search: |
;318/602-632,430-434,560,561,570-573 ;180/65.8 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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196 20 439 |
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Dec 1996 |
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DE |
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01304511 |
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Dec 1989 |
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JP |
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Primary Examiner: Ip; Paul
Attorney, Agent or Firm: Feiereisen; Henry M.
Claims
What is claim is:
1. A method of damping mechanical oscillations of at least one
shaft of a machine tool, manufacturing machine or robot, said
method comprising the steps of: measuring an actual position Value
of a shaft using at least one sensor and/or measuring system;
determining an actual speed of the shaft from the actual position
value through differentiation; supplying the actual speed of the
shaft as an input signal to each of a plurality of feedback
elements; and tuning each of the feedback elements to a specific
oscillation frequency range of the shaft oscillations that is to be
damped, each feedback element providing an output signal that is
negatively coupled arid applied to a desired speed signal of a
motor speed controller of a driving motor.
2. The method of claim 1, wherein each of the feedback elements is
a band-pass or high-pass element.
3. The method of claim 1, wherein each of the feedback elements is
differential element with first-order delay or a differential
element with second-order delay or higher order.
4. A method of damping the mechanical oscillations of at least one
shaft of a machine tool, manufacturing machine or robot, said
method comprising the steps of: determining an actual acceleration
of a shaft by using at least one sensor and/or measuring system;
supplying the actual acceleration of the shaft as an input signal
to each of a plurality of feedback elements; and tuning each of the
feedback elements to a specific oscillation frequency range of the
shaft oscillations that is to be damped, each feedback element
providing an output signal that is negatively coupled and applied
to a desired speed signal of a motor speed controller of a driving
motor.
5. The method of claim 4, wherein each of the feedback elements is
a proportional element having a first-order delay or a proportional
element having a second-order or higher-order delay.
6. The method of claim 4, wherein the supplying step includes the
step of determining the actual speed of the shaft from the actual
acceleration through integration, wherein each of the feedback
elements is a differential element having a first-order delay or a
differential element having a second-order or higher order
delay.
7. A method of damping the mechanical oscillations of at least one
shaft of a machine tool, manufacturing machine or robot, said
method comprising the steps of: measuring an actual position value
of an shaft using at least one sensor and/or measuring system;
determining an actual acceleration of the shaft from the actual
position value through second-order differentiation; supplying the
actual acceleration of the shaft as an input signal to each of a
plurality of feedback elements; and tuning each of the feedback
elements to a specific oscillation frequency range of the shaft
oscillations that is to be damped, each feedback element providing
an output signal that is negatively coupled and applied to a
desired speed signal of a motor speed controller of a driving
motor.
8. The method of claim 7, wherein each of the feedback elements is
a proportional element with first-order delay or a proportional
element with second-order delay or higher order.
9. The method of claim 7, wherein the supplying step includes the
step of determining from the actual acceleration the actual speed
of the shaft through integration wherein each of the feedback
elements is a differential element with first-order delay or a
differential element with second-order delay or higher order.
10. A method of damping mechanical oscillations of at least one
shaft of a machine tool, manufacturing machine or robot, said
method comprising the steps of: determining an actual speed of a
shaft by using at least one sensor and/or measuring system;
supplying the actual speed of the shaft as an input signal to each
of a plurality of feedback elements; and tuning each of the
feedback elements to a specific oscillation frequency range of the
shaft oscillations that is to be damped, each feedback element
providing an output signal which is negatively coupled and applied
to a desired speed signal of a motor speed controller of a driving
motor.
11. A method of damping mechanical oscillations of at least one
shaft of a machine tool, manufacturing machine or robot, said
method comprising the steps of: measuring an actual acceleration of
a shaft by a first type of sensor and/or measuring system;
measuring an actual speed of the shaft by a second type of sensor
and/or measuring system; supplying the actual acceleration of the
shaft as an input signal to a first set of feedback elements to
provide an output signal that is negatively coupled and applied to
a desired speed signal of a motor speed controller of a driving
motor; supplying the actual speed of the shaft as en input signal
to a second set of feedback elements to provide an output signal
that is negatively coupled and applied to a desired speed signal of
a motor speed controller of a driving motor; and tuning each of the
feedback elements to a specific oscillation frequency range of the
shaft oscillations that is to be damped, wherein each of the first
and second sets of feedback elements includes at least one feedback
element.
12. A method of damping mechanical oscillations of at least one
shaft of a machine tool, manufacturing machine or robot, said
method comprising the steps of: determining an actual state
variable of the shaft; supplying the actual state variable of the
shaft as an input signal to each of a plurality of feedback
elements; and tuning each of the feedback elements to a specific
oscillation frequency range of the shaft oscillations that is to be
damped, each feedback element providing an output signal which is
negatively coupled and applied to a desired speed signal of a motor
speed controller of a driving motor.
13. The method of claim 12, wherein the determining step includes
the steps of measuring an actual position value of the shaft by a
measuring means, and ascertaining the actual state variable as an
actual speed of the shaft obtained from the actual position value
through differentiation.
14. The method of claim 12, wherein the determining step includes
the steps of measuring an actual acceleration of the shaft, and
ascertaining the actual state variable as an actual speed of the
shaft obtained from the measured actual acceleration through
integration.
15. The method of claim 12, wherein the determining step includes
the step of ascertaining the actual state variable as a measured
actual acceleration of the shaft.
16. The method of claim 12, wherein the determining step includes
the steps of measuring an actual position value of the shaft, and
ascertaining the actual state variable as an actual acceleration of
the shaft obtained from the measured actual position value through
second-order differentiation.
17. The method of claim 12, wherein the determining step includes
the step of ascertaining the actual state variable as a measured
actual speed of the shaft.
18. Apparatus for damping mechanical oscillations of a shaft of a
machine tool, manufacturing machine or robot having a driving
motor, comprising: plural feedback elements, each feedback element
being adapted to generate an output signal that is negatively
coupled and applied to a desired speed signal of a motor speed
controller of the driving motor; measuring means for measuring a
shaft variable; means for determining an actual shaft variable from
the measured shaft variable by calculation; means for supplying the
calculated shaft variable as an input signal to each feedback
element; and means for tuning each feedback element to a respective
oscillation frequency range of the shaft's oscillations that is to
be damped.
19. The apparatus of claim 18, wherein a tuned band-pass filter is
used as a feedback element for one of the oscillation frequency
ranges of the shafts oscillations that is to be damped.
20. The apparatus of claim 18, wherein a tuned high-pass filter is
used as a feedback element for one of the oscillation frequency
ranges of the shaft's oscillations that is to be damped.
21. The apparatus of claim 18, wherein a tuned differential element
having at least a first-order delay is used as a feedback element
for one of the oscillation frequency ranges of the shaft's
oscillations that is to be damped.
22. The apparatus of claim 18, wherein a tuned proportional element
having at least a first-order delay is used as a feedback element
for one of the oscillation frequency ranges of the shaft's
oscillations that is to be damped.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims the priority of German Patent Application,
Ser. No. 102 46 093.0, filed Oct. 2, 2002, pursuant to 35 U.S.C.
119(a)-(d), the disclosure of which is incorporated herein by
reference.
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for damping
mechanical oscillations of shafts of a machine tool, manufacturing
machine or robot by providing feedback elements that apply a
negative feedback output signal from each feedback element to the
desired rotational speed value of a speed controller for a motor
driving the shaft.
Modern machine tools, manufacturing machines or robots frequently
produce undesired oscillations, particularly about the shafts and
in particular the NC-shafts (numerical-control shafts) of the
machine. It is to be understood by persons skilled in the art that
the term "machine" is used here in a generic sense and the
principles described in the following description with respect to
machine are equally applicable to robots. The oscillations are
caused by poorly damped mechanical resonances in the mechanical
system of the machine. As a result, the speed of the shaft is
increased above or reduced below the point where the undesired
resonance occurs. Such resonance produces undesirable chatter marks
that mechanically strain the machine, and leads to a decrease in
the processing accuracy. As a rule, the mechanical system of the
machine has several areas of resonance, which have respective
limited frequency ranges.
In a conventional drive controller, a superordinated
position-control circuit provides a desired motor speed to a
subordinated speed controller for rotation of the machine shafts.
In the event a respective gain is selected for the speed
controller, the mechanical resonances of the mechanical system of
the machine are clearly noticeable in the form of drops and
increases in the amplitude excursions of the reference frequency
response in the speed control circuit. Only a very limited damping
of these resonance oscillations is possible with the position
control means available. This conventional approach is unsuitable
for implementing an effective damping of the oscillations caused by
mechanical resonance. The result is inadequate machine dynamics and
chatter marks, as well as the gain in the position controller being
limited to just a small adjustable range.
German Pat. No. DE 196 20 439 C2 discloses a method of damping
mechanical oscillations in machine tools and robots, saw-tooth
oscillations in particular, as well as rotational oscillations. Two
control variables are determined by two acceleration detectors and
fed back via the controller to a drive controller as a desired
value.
It would therefore be desirable and advantageous to provide an
improved method and apparatus of damping mechanical oscillations,
to obviate prior art shortcomings and to exhibit limited
oscillation frequency ranges for shafts of machine tools,
manufacturing machines or robots, while being simple and
cost-efficient.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, a method of
damping the mechanical oscillations of at least one shaft in a
machine tool, manufacturing machine or robot, includes the steps of
measuring an actual position value of a shaft using at least one
sensor and/or measuring system, determining an actual speed of the
shaft from the actual position value through differentiation,
supplying the actual speed of the shaft as an input signal to each
of a plurality of feedback elements, with each feedback element
providing an output signal from each of the feedback elements that
is negatively coupled and applied to a desired speed signal of a
motor speed controller for the motor driving the shaft, and tuning
each of the feedback elements to a specific oscillation frequency
range of the oscillations of the shaft that are to be damped.
According to another feature of the present invention, tuned
band-pass or high-pass elements tuned to the respective oscillation
frequency range to be damped can be used as feedback elements.
Band-pass or high-pass filter elements can easily be implemented
using typical mathematical calculation programs in use today. The
filter is constructed so as to provide a suitable gain and phase
margin in the oscillation frequency range that is to be damped.
This determines the range of frequencies that are controlled.
According to another feature of the present invention, a
differential element tuned to the respective oscillation frequency
range to be damped and having a first-order (DT1) or a differential
element having a second-order (DT2) or a higher-order delay can be
used. DT1-elements, DT2-elements and differential elements of a
higher order, are able to differentiate below a limit frequency and
to provide an adequate phase margin in a closed control circuit,
thereby protecting the stability of the control circuit. In some
instances, it is advantageous if the delay of second-order or
higher-order has a slight damping effect and thus produces a rise
in the resonance.
According to another feature of the present invention, instead of
using the sensor and/or measuring system for measurement of the
actual shaft position value, a sensor and/or measuring system can
be used for measurement of the shaft acceleration, or the
acceleration is determined by second-order differentiation from the
shaft position value. The acceleration is then used as an input
variable for the respective feedback element. Resonance
oscillations are especially easy to detect in the acceleration of
the shaft. Acceleration can advantageously be directly measured on
the shaft or areas which are caused to oscillate as a consequence
of a shaft movement.
According to another feature of the present invention, a
proportional element tuned to the respective oscillatory frequency
range to be damped and having a first-order delay or a second-order
or higher-order delay can be used as a feedback element. Of course,
it is also possible to calculate the speed of the shaft from the
acceleration by integration and then to use as feedback elements
the DT1-elements, DT2-elements and differential elements having a
higher-order delay. A drawback of this approach is, however, an
increase in computation time compared to a direct processing of the
shaft acceleration in the feedback elements. In certain cases,
however, this approach may still be advantageous, for example when
the use of proportional elements is undesirable.
According to another feature of the present invention, instead of a
sensor and/or measuring system for measuring position values for
the shaft, a sensor and/or measuring system may conceivably be used
as well, for measuring the actual speed of the shaft. The actual
speed of the shaft is then fed directly to the feedback elements as
an input variable. The determination of the actual shaft speed by
differentiation of the actual position value of the shaft can thus
be eliminated by directly measuring the actual speed.
According to another feature of the present invention, in addition
to or instead of the sensor and/or measurement system for
measurement of the actual shaft position, further sensors and/or
measurement systems can be used, especially those for measuring
shaft acceleration and/or shaft speed, and the respective measured
shaft variable or a calculated variable produced from measured
variables is supplied as input variable to a respective one of sets
of feedback elements, whereby each of the sets of feedback elements
has at least one feedback element. By the use of not just one but
multiple measured variables as input variables for a respective
separate set of feedback elements, for example an actual position
value as well as shaft acceleration, a particularly good damping of
the mechanical shaft oscillations can be achieved.
BRIEF DESCRIPTION OF THE DRAWING
Other features and advantages of the present invention will be more
readily apparent upon reading the following description of
currently preferred exemplified embodiments of the invention with
reference to the accompanying drawing, in which the sole FIG. 1 is
a schematic block diagram illustrating the components of the
subject matter of the present invention:
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The depicted embodiment is to be understood as illustrative of the
invention and not as limiting in any way. It should also be
understood that the drawings are not necessarily to scale and that
the embodiments are sometimes illustrated by graphic symbols,
phantom lines, diagrammatic representations and fragmentary views.
In certain instances, details which are not necessary for an
understanding of the present invention or which render other
details difficult to perceive may have been omitted.
Turning now to FIG. 1, there is shown a schematic block diagram
illustrating the components of the subject matter of the present
invention. A motor 1 drives a not shown shaft of a machine via a
mechanism 2. An actual speed V.sub.m.sub..sub.-- .sub.actual of the
motor 1 and an actual position value X.sub.p.sub..sub.--
.sub.actual is measured by a suitable measuring system. The motor
speed V.sub.m.sub..sub.-- .sub.actual is controlled by a motor
speed controller 3, which has the difference between the motor
speed V.sub.m.sub..sub.-- .sub.actual and the desired motor speed
V.sub.m.sub..sub.-- .sub.desired as an input variable E and on the
output side provides a control output signal A to a motor
controller 4 that controls the motor speed V.sub.m.sub..sub.--
.sub.actual through an output current 1.
The motor speed controller 3 may be implemented as a conventional
proportional integral-action controller. A desired motor speed
position value V.sub.p.sub..sub.-- .sub.desired is given by a
superordinated position control circuit (not shown for ease of
illustration) for position control of the shaft.
In the exemplified embodiment shown here three oscillation
frequency ranges or resonance areas of the mechanical systems of
the machine are assumed.
An actual shaft speed V.sub.p.sub..sub.-- .sub.actual is calculated
from the actual shaft position value X.sub.p.sub..sub.--
.sub.actual by means of a differentiation element 5 and delivered
to the feedback elements R1, R2, R3. The output signals B1, B2, B3
of the feedback elements R1, R2, R3 are negatively coupled and
applied to a desired motor speed position value V.sub.p.sub..sub.--
.sub.desired, which is generated by a superordinated position
control circuit (not shown for ease of illustration), to form on
the output side a desired motor speed signal V.sub.m.sub..sub.--
.sub.desired.
A feedback element is provided for each oscillation frequency range
to be damped. Thus, the assumed three oscillation frequency ranges
to be damped in the present exemplified embodiment requires
therefore three feedback elements R1, R2, R3. FIG. 1 illustrates
the parallel control structure and feedback structure,
respectively. To suppress even more oscillation frequency ranges or
resonance areas, the arrangement shown is supplemented by further
feedback elements or feedbacks connected in parallel and tuned to
the respective oscillation frequency ranges to be damped.
When selecting suitable feedback elements, care should be taken to
provide them with a suitable gain and phase margin in the range of
the oscillations that are to be suppressed. Such a feedback element
can readily be realized as a band-pass filter or a high-pass
filter, for example, in the form of a finite impulse response or an
infinite impulse response filter. Suitable filters can be easily
calculated today, or the filter coefficients defined, using
commercially available filter design programs. In the design of the
feedback element, care should be taken so that the phase margin in
the closed control circuit is not too small, otherwise the
stability of the control circuit is jeopardized.
An example for use as feedback elements with band-pass response
includes differential elements with second-order delays, so-called
DT2 elements, which have a transfer function in the form:
##EQU1##
wherein the parameter "s" relates to the complex circuit frequency
while the frequency behavior of the DT2 element can be
parameterized with the assistance of the time constant "T" and the
damping "d".
Examples for the transfer function of high-pass filters include:
##EQU2##
wherein
T is the time constant,
T.sub.1 is the denominator time constant,
T.sub.2 is the numerator time constant,
d.sub.1 is the denominator damping value, and
d.sub.2 is the numerator damping value.
The parameter s relates hereby to the complex circuit frequency
while the time constants T, or T.sub.1, T.sub.2, d.sub.1 and
d.sub.2 are used to parameterize the frequency behavior of the
high-pass elements. Feedback elements of this type operate in lower
frequency ranges by differentiation, i.e., they display high-pass
characteristics and allow an adequate phase margin for the control
circuit.
Of course, other feedback elements may also be used. In the
exemplified embodiment of FIG. 1, the feedback elements R1 and R2
are realized as band-pass elements, while the feedback element R3
is implemented as differential element DT1 having a first-order
delay.
For specific phase margins it may be necessary to include
additional filters in the feedback element, for example low-pass or
notch filters.
The parallel control structure shown provides easy set up of the
mechanism. Initially feedback elements can be deactivated, the
feedback elements R2 and R3 for example. Only the feedback element
R1 is activated, and correspondingly parameterized. Once the
feedback element R1 has been parameterized, the feedback element R2
is additionally activated and parameterized. Activation and
parameterization of the feedback element R3 follows thereafter.
Instead of taking the actual shaft position X.sub.p.sub..sub.--
.sub.actual as feedback value, it is also possible to use suitable
sensors or measuring systems to directly measure shaft
acceleration, or to use the directly measured actual shaft speed
V.sub.p.sub..sub.-- .sub.actual. If the acceleration is selected as
the input variable in place of the actual shaft position
X.sub.p.sub..sub.-- .sub.actual, then the actual shaft speed
V.sub.p.sub..sub.-- .sub.actual can be calculated through
integration, and supplied to the feedback elements or, in the event
that the provision of an additional integrator is not desired,
proportional elements (PT1) having first-order delay, or
proportional elements (PT2) having second-order delay can be used
in place of the DT1 or DT2 feedback elements, and the measured
acceleration can be supplied directly to the PT1 or PT2 elements.
The transfer functions of such elements are well known in the art,
and therefore a further discussion thereof is omitted for the sake
of simplicity.
Instead of an explicit measurement of the acceleration of the
shaft, it is also conceivable to calculate the shaft acceleration
through second-order differentiation of the actual position value
X.sub.p.sub..sub.-- .sub.actual and to subsequently supply it as
input variable to the PT1 elements or PT2 elements.
If the actual shaft speed V.sub.p.sub..sub.-- .sub.actual is taken
as the input value in place of the actual position value
X.sub.p.sub..sub.-- .sub.actual, the differentiating element 5 can
be eliminated.
Of course, it is not necessarily required to use only one
measurement variable, e.g. actual position value, actual speed and
acceleration of the shaft, as input variable of the control
elements; Rather, it is also possible to use, e.g. actual position
value and acceleration of the shaft simultaneously as controlled
variables, or variables calculated therefrom as input variables.
The actual position value of the shaft is, for example, supplied to
a first set of feedback elements as input variable, and the
acceleration is supplied to a second set of feedback elements as
input variable. A set of feedback elements is hereby comprised of
at least one feedback element. Basically, any desired combination
of input variables is possible.
Furthermore, the parallel control structure depicted allows a
simple set up of the machine. For example, the feedback elements R2
and R3 can initially be deactivated, with only feedback element R1
activated and correspondingly parameterized. Once the feedback
element R1 has been parameterized, the feedback element R2 is
additionally activated and parameterized. Activation and
parameterization of the feedback element R3 follows thereafter.
While the invention has been illustrated and described in
connection with currently preferred embodiments shown and described
in detail, it is not intended to be limited to the details shown
since various modifications and structural changes may be made
without departing in any way from the spirit of the present
invention. The embodiments were chosen and described in order to
best explain the principles of the invention and practical
application to thereby enable a person skilled in the art to best
utilize the invention and various embodiments with various
modifications as are suited to the particular use contemplated.
What is claimed as new and desired to be protected by Letters
Patent is set forth in the appended claims and their
equivalents:
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